Undersea optical communication systems include land-based terminals containing transmitters and receivers connected by a cabled-fiber-transmission medium that includes periodically spaced repeaters, which contain optical amplifiers whose purpose is to compensate for the optical attenuation in the cabled fiber. As the repeaters are usually placed undersea and away from power sources, power must be supplied remotely to the repeaters. The cabled fiber therefore usually contains a copper conductor to carry electrical power to the repeaters from the terminals. These undersea systems serve to carry optical communication signals (i.e., traffic) between the terminals. The traffic on these systems can consist of voice, data, television, Internet traffic, international telephone traffic, etc. Consequently, the revenue lost when the system is down can be significant. Therefore, these systems must have high reliability and availability.
To provide increased flexibility in undersea network architecture beyond simple point-to-point interconnection between land-based terminals, a branching unit is provided, which allows traffic to be split or switched to/from multiple landing points. Conventional branching units typically manage the cabled-fiber interconnections and the power conductor paths among three cables. The latter is necessary to maintain as much traffic carrying capability when a fault occurs in one of the three cable legs, which increases the availability of the system.
A power-switched branching unit is configured to allow re-routing of electrical power from the terminals in the presence of a fault in one of the cables, so that two of the three cable legs in a branched system can still be powered. Such a power-switched branching unit usually has three operating states: normal, alternate-normal, and grounded-trunk. The power-switched branching unit can be configured in any of these three states by the appropriate power-up sequencing from the terminals of the three legs. The reconfiguration of the branching unit is typically performed by a relatively complex series of relays, which significantly adds to the cost and complexity of the device.
Accordingly, it would be desirable to provide an undersea branching unit that does not require such complex active power control.